The present invention pertains to packaging film, and more particularly to a thin polymeric film suitable for replacing polyvinyl chloride film especially in packaging and labeling applications.
Polyvinyl chloride (PVC) has long been used in many applications in the packaging art. One particularly widespread application for PVC is the use of such material as an overwrap material for trayed retail cuts of meat and other food products in a retail environment such as a supermarket.
PVC has several desirable properties for this use. For example, it has excellent optics and good elasticity and stretch properties at use temperatures.
Unfortunately, PVC also has several disadvantages, including the production of hydrogen chloride gas during heat sealing and the generally corrosive effects of such gases in the packaging room.
It would be of great benefit to the packaging industry, and particular to applications requiring an instore film for overwrapping trayed food products, to provide a film with many of the advantages of PVC but without the disadvantages described above.
PVC is also used in producing labels for cans and bottles. It would also be of benefit to the label industry to provide a film which can be used as a label on a rigid container such as bottles and cans, but without the disadvantages of PVC.
Films or laminates used as label material for the labels of beverage bottles and the like are preferably monoaxially oriented in order to permit a tight label to be produced around the bottle or vessel, without undesirable wrinkling and shrinking of the label which can occur with some biaxially oriented films. These label films can also be used to produce band type seals for tamper evidence. Such label material ideally possesses several properties making it particularly useful for this end use.
For example, the material should have the required stiffness (i.e. higher modulus) to permit the use of the film or laminate in a roll stock form in conjunction with label manufacturing apparatus. Printability of the label is also desirable, as well as excellent optical properties.
The inventor has discovered that a relatively thin polymeric film, including a layer of a polyolefin, and more preferably very low density polyethylene (VLDPE), combined with a layer of styrene butadiene copolymer (SBC), produced by hot blowing and then stretch orienting the extruded film, exhibits excellent elasticity, toughness, stretch and optical properties.
Processes for producing oriented films, and oriented films themselves are disclosed in many patents including the following patents of interest.
U.S. Pat. No. 3,456,044 (Pahlke) mentions thin films of thicknesses less than 1 mil such as 0.5 mils, and discloses a double bubble method for biaxially orienting thermoplastic films including the steps of producing a primary tubing which is inflated by introducing air into the interior thereof, and a cooling ring 22, as well as squeeze rolls 34 and 28, with rolls 34 having a greater speed than rolls 28. Between the two pairs of squeeze rolls is a reinflated secondary bubble. If annealing is desired, the tubing can be reinflated to form a bubble 70.
U.S. Pat. No. 3,555,604 (Pahlke) is a patent based on a divisional application which was derived from the same priority application as the '044 patent described above, and discloses the same information described above for the '044 patent.
U.S. Pat. No. 4,258,166 (Canterino et al) discloses a uniaxially oriented plastic film material with improved strength and clarity in the direction of orientation preferably comprising homopolymers and copolymers of ethylene.
U.S. Pat. No. 4,355,076 (Gash) discloses monoaxially oriented polypropylene film laminated to a monoaxially oriented high density polyethylene film, the films produced by for example tubular blowing.
U.S. Pat. No. 4,440,824 (Bonis) discloses a thermoformable coextruded multilayer structure useful for thermoforming into containers, the structure having polyolefin coextruded with a high impact polystyrene layer. A five layer structure is shown.
U.S. Pat. No. 4,464,439 (Castelein) discloses a coextruded laminate having a sheet of polypropylene and a sheet of a mixture of high impact polystyrene, crystalline polypropylene, and styrene/dienic monomer block copolymer.
U.S. Pat. No. 4,626,455 (Karabedian) discloses a multilayer sheet and sleeve label for bottles, the sheet being a skin layer/brittle polystyrene foam layer structure, the skin layer comprising a polyolefin, a block copolymer of butadiene and styrene as compatability agent, and polystyrene.
U.S. Pat. No. 4,879,177 (Boice) discloses a monoaxially oriented shrink film having a core layer of butadiene styrene copolymer, outer layers of ethylene propylene copolymer, and intermediate bonding layers of ethylene copolymer.
It is an object of the present invention to provide a thermoplastic film useful as an overwrap material for trade retail cuts of meat and other food products in a super market or other retail environment.
It is also an object of the present invention to provide a thermoplastic film useful in forming labels or tamper evident bands for vessels such as bottles, cans, and the like.
It is also an object of the present invention to provide a film having excellent optical properties, specifically excellent gloss and clarity.
It is also an object of the present invention to provide a film which can be either primarily monoaxially oriented, or biaxially oriented to substantially the same extent in both its transverse and longitudinal directions.